Method of making a memory matrix



March 7, 1967 P. H. CRAIG METHOD OF MAKING A MEMORY MATRIX Filed July 2, 1965 FIGS 'portion of the other set of wires.

United States Patent 3,307,245 METHOD OF MAKING A MEMORY MATRIX Palmer H. Craig, Florida Atlantic University, College of Science, Boca Ratou, Fla. 33432 Filed July 2, 1963, Ser. No. 292,310 Claims. (Cl. 29155.5)

The present invention relates to a method of manufacture of a memory matrix structure, and the structural nature of a new memory matrix. More particularly, the invention relates to an arrangement or array comprising a set of horizontal conductors and a set of vertical conductors arranged in a frame or matrix so as to form a crosswork of wires. One or the other set of wires is insulated by a coating of insulation, while the other set of wires is bare. The sets of wires are in physical and mechanical contact with each other, but due to the insulation there is no electrical contact therebetween. The matrix structure of the invention is such that the toroidal magnet core or film so encircles the wires that at their points of crossing the Wires thread through the toroidal -film.

Accordingly, the present invention is directed to a method consisting in the forming of a film, and comprises first insulating the bare set of wires at the portions thereof between and about points where they cross the other set of wires. This is accomplished by spraying an insulating plastic coating over the matrix, while the points of the crossings are marked by masking material during the spraying operation. After the spraying is thus accomplished, the masking is removed and the wires in the region of the crossing are coated with a conductive material. The coating of conductive material encircles the two wires in contact with the bare portion and the insulation of the other wire to form a mechanical connection. The matrix is then subjected to an electroplating operation in which the bare wires are connected together to form the cathode during such operation, while magnetic material is plated or coated onto the matrix.

In addition to the above method and incident to the invention, in order to reduce the effect of eddy currents, several coatings or films, each separated by an insulating material or layer, may be provided about the single film produced by the above method, and are applied to provide a multiple lamination.

The matrix structure is an improvement, and is new compared with known matrix structures of the prior art in that at least one wire is bare as it threads though a toroid and is connected conductively to the toroidal film. The advantage of the new structure of the present invention is that it may be manufactured more cheaply than many other structures, and has improved and superior characteristics as are disclosed and described herein-below.

One form of the present invention further provides a novel and improved structural effect for providing a much greater and effective contact area between the two conductors of the matrix so that while the wires of each set are generally perpendicular to each other, there is a small but substantial portion of one set of wires that is generally parallel and co-linear with the corresponding This configuration may be denominated as a dog-leg structure or configuration, and is constructed by being preformed so that when the two sets are contacted at the dog-leg portion of one set with the straight portion of the other set, there is much greater contact area between the two sets of the matrix. The dog-leg arrangement provides a resultant output for a given pulse input that is approximately 100 times greater than what may be expected when there is the simple and well-known crossing of the two conductor sets.

3,307,245 Patented Mar. 7, 1967 It is an object of the invention, therefore, to provide a new and improved method of manufacture of a matrix structure.

It is also an object of the invention to provide a new an dimproved matrix comprising a dog-leg arrangement of wires forming the matrix.

The above and other objects and advantages of the invention will become apparent upon full consideration of the following detailed description and accompanying drawings in which:

FIGURE 1 is a plan view of a portion of a matrix formed by the method of the present invention;

FIGURE 2 is a vertical cross-sectional view taken along lines 22 of FIG. 1, and showing the matrix of the invention;

FIGURE 3 is a horizontal cross-sectional view taken along lines 33 of FIG. 1 and showing the matrix of the invention; a

FIGURE 4 is a plan view of a portion of a matrix having a dog-leg unit formed of a thin-film plated toroidal core in accordance with a feature of the invention; and

FIGURE 5 is a hysteresis curve showing the B-H characteristics of the dog-leg unit of the present invention.

Referring to the figures of the drawings, there are provided a set of horizontal conductors 10 at least two of which are identified further as 12 and 14-, and a series or set 16 of vertical conductors at least two of which are 18 and 20. One of these sets 16 is formed of originally uninsulated or bare wire of conductive strips, while the other set 10 is processed to provide insulation 24 in at least adjacent or sub-adjacent portions thereof where they are proximate to the other set of conductors which areas are defined as junction areas 29.

A mask having apertures positioned adjacent the junction areas is positioned over the matrix formed by sets 10, 16. An insulating film is applied through the apertures by spraying or applying an insulating plastic coating. The mask is removed.

The two sets 10, 16 of conductors of the matrix mechanically touch or contact each other and are held taut in a framework (not shown) during the processing in forming the resultant matrix. After the matrix comprising the sets 10, 16 has been formed in the framework as above described, the set 16 of conductors is provided with insulation in all portions not contained within the areas at the junction areas 29 of conductor sets 10, 16 in FIG. 1 which areas would be shielded and not subject to spray, dip or the paint of the insulating materials. The insulated portions 26 are shown in FIG. 3.

The next step of the invention is to place or apply a conductive film 28 over the junction areas 29 at the junctions or intersections of the conductors 12, 14 and 18, 20. This conductive film 28 covers both sides and about the edges of the respective sets of conductors, and, if the conductors are strips or otherwise configured conductors, the conductive film covers the entire surface of both conductors about the junction area as shown by coating film 28 of FIG. 3. Obviously, the conducting film electrically engages the conductor 18 as shown in FIG. 3. If all conductors of set 16 were temporarily joined together at their ends, the conductive film 28 would therefore act as a cathode in a substantial and effective matrix form, or rather as a series of cathodes all electrically interconnected, making it possible to electrodeposit or electroplate any desired magnetic material 30 or alloy thereon. Since the area within the junction area of conductor sets 10', 16 is non-insulated and the electroplated material covers not only the conductive surface 28 but also the uninsulated portions or junction areas 29 of the conductor sets 16, it is thus deposited as illustrated in FIG. 3 and also in section 22 of FIG. 2. The electrodeposited magnetic material 30 forms a complete enclosure for the junctures of the conductor sets 10, 16. It is, of course, understood that the conductors may be of any configuration including round, square, rectangular, or correspondingly strip-type materials, and may contain multiple layers 24a similar to coating 24 alternatively arranged with material 30a similar to material 30.

The method for producing a magnetic memory matrix in accordance with the present invention includes electrodeposition of the magnetic material 30, such as HyMu 80 material, about the junction areas 29 of a series or sets of wires or conductive strips that form the matrix. This method differs essentially from conventional methods in that these sets of wires or strips are not associated with backing plates during the normal processing in producing the matrix, although they can 'be attached to such plates after they have been processed. In the method of the invention, the electromagnetic equivalent of toroidal magnetic cores being threaded by conductors is now obtained in practicing the present invention by a much simpler and cheaper method.

By current concidental or other methods it is possible to magnetize the magnetic material 30 which has been deposited at the junction areas 29. Thus magnetic material 30 effectively forms a toroid. In many respects this is mechanically equivalent to the result accomplished by threading conductors through a toroid and provides a simple and inexpensive method for accomplishing this effect and result.

The insulation 24 of conductor set may be of any desired form such as enamel, glass, plastic, etc. It is of course desirable to use an insulation to which the conducting film will adhere. One method of applying the conductive film is to use the double-nozzle silver spray method outlined in publications such as Metalizing of Plastics, by Harold Narcus (Rheinhold Publishing Co.). Materials other than silver such as copper, conductive epoxys, conductive paints, and the like, may also be applied to the matrix for the purpose of producing cathode spots electrically connected to the conductor set 16 for the purpose of electroplating these spots.

Several methods of plating a memory matrix have been described and disclosed above and these methods depend on how and in what manner the toroid is made. The core or toroid of FIG. 4 may be generally one-half inch wide, since short lengths of the conductors may be bent into parallelism and arranged to form a dog-leg structure about which the magnetic material 30 is formed. In the dog-leg arrangement the conductors 12a and 18a are positioned so that they are generally parallel over a small distance, as shown. It is desirable to reduce the width of the core without affecting the output of the core. It therefore follows that an increase in the thickness of the toroid effectively and equivocally compensates for any reduction in the width of the toroid, but the bent or dog-leg configuration has improved electrical characteristics when used as a matrix memory.

The toroid 30 is then plated over the intersection of two conductor wires forming the matrix, which conductor wires may be of 26 gauge. In other words, the toroid is plated or electrodeposited over two 26 gauge wires that have been coated with plastic, and the toroid is formed of a maximum diameter of 0.50 inch at the center and is 0.3 inch long. It may be seen that decreasing the width of the toroid decreases the core area which, in turn, decreases the volt-second output. Since it is expected that the speed of switching depends primarily upon the plating thickness, a shorter toroid will produce a lower signal output voltage. Thus a long, thin toroid of the type shown can be made or a toroid having various thicknesses may be used. If a shorter toroid is used, there are at least two methods of doing this. One method is to plate over thin metallic wires wound around a junction matrix, a method which may present various production problems. Another method is to plate successive layers with proper interlamination resistance between each layer.

It is considered that a simple matrix may be built according to the invention that at least equals the fast ferrite memories now in use, and it is capable of prediction that the matrix of the invention may have some measure of an improved and faster memory than the ferrites now used. It is easily resolved that the cost of the matrix construction of the invention is much less than those of the prior art.

Inasmuch as it may be required and desirable to place several layers of magnetic material 30, 30a over the various junctions in order to build up the output thereof, it has been found that further investigate theoretical considerations point toward the value of interlamination insu=lation24a required and essential to hold .eddy currents to desirable values.

Using basic developments as described above, matrices are prepared for use to provide write-in or read-out data on a thin film magnetic memory. Considerable development has been directed to the development of the matrices in order that the word or clock drives, the digit drives, and the sense loops may be placed as close as possible to each other from the standpoint of at least the two necessary layers of the matrix, and also to place these matrices as close as possible to the actual magnetic film. This is achieved by providing at least separations be- .tween the x-drives and the y-drives of the order of 0.00025 inch, and this same order of separation exists between these drives and the sense loops.

In accordance with a feature of the present invention, as many as 20 such conductors per linear inch in each direction may be used, which would therefore provide for 400 bits of informations per square inch. Typical arrangements of such an embodiment include providing a film plated on either aluminum or non-magnetic stainless steel substrates from which has been obtained H values from approximately 0.6 oersted to several oersteds depending upon the composition of the plated material. A large number of alloys has been tested to produce this general method of construction to achieve an operative result. These alloys include various percentages of nickel and iron, and also various Permalloys including molybdenum alloys, cobalt alloys, compositions equivalent to Supermalloy, and many others known commercially. The necessary plating baths have been developed for these materials, and for such materials optimum plating current temperatures, hydrogen ion concentrations and graphs are thus prepared showing the plating time re quired to produce different thicknesses of such films. The composition of various Permalloys and also Supermalloys and other similar magnetic materials may be obtained from such sources as Table 2l, pp. 30-31 of IqMagnetic Amplifiers, by H. F. Storm (Wiley & Sons,

A wide range of H values is available as well as ratios of B /B It is not difficult under laboratory conditions to obtain extreme squareness of the hysteresis curve, nor is it difiicult to obtain alloys of materials like molybdenum commercially which is quite difficult to produce in alloy form by vacuum deposition. There has been found to be a substantial and remarkable degree of reliability of the magnetic characteristics for the various runs of these types of materials used in matrices in accordance with the invention. Such tests under various conditions and using various materials indicate a uniformity varying less than From the standpoint of temperature variations, the method of the invention has marked advantages over ferrites and probable advantages over wound tape cores for the reason that the latter may vary the separations between layers and the stress factors to a greater extent than plated type cores.

In connection with cores, it should be pointed out that it is found unnecessary to anneal most of the cores or films from a selection of substrates, such as stainless steel, having favorable physical characteristics and which may have a temperature co-efficient of expansion almost identical to that of the plated material and with as much elimination as possible of the stresses of the plated material when a substrate expands over wide temperature ranges. Both cores and films are plated in the presence of a magnetic field which may be controllably varied or selected in the range between oersteds to well over 500 oersteds, as is known and suggested from a publication by N. V. Koteinikov, Department of Physics, Moscow State University, page 35 (1957).

There are several know-n brightening agents such as Udylite Nickel Brightener commercially available as an additive agent in plating baths. These agents are materials which normally consist of such materials as saccharin (700 mg/1.), m-benzenedisulphonic acid, sodium salt, p-toluenesulphonamide 654 mg./liter; quinoline 85 mg./l.; nicotinam-ide 50 g./l.; beta unsaturated esters; and such saturated compounds as peradine and aniline.

It is generally recognized that the kinetics of polarization is dependent on the cathode adsorption of additive agents. Also the addition agents play a role in the sulphur and nitrogen content of deposits, as well as in leveling. It has been suggested in the prior art that leveling and brightening are similar, the latter being a microleveled random deposition of crystalline seeds smaller than the wave length of light. The action of organic additives is thought by those authors to be an interaction of organic molecules and nickel ions, thus decreasing the size of growth centers in electrodeposition.

It is also thought by some investigators that the theory of electron-pairs may play an important role, since this theory involves the attachment of organic compounds to the nickel surface depending upon the presence of the molecule of available electron pairs able to interact with metallic atoms.

Since magnetic properties are greatly influenced by stresses, a number of workers in the prior art have in vestigated stress-reducing agents. In this connection such proprietary products as Nuodex SC stress control agent, made by Nuodex Products Division, Heyden Newport Chemical Corporation, has been used as a stress-reducing agent in electrodeposition. The chemical nature and eifect of such agents is considered to provide an effective reduction in further deposition in the new vicinity particularly when saccharin is used. It is assumed that saccharin being an organic molecule with a polar group attached will be attracted to high-potential peaks on the cathode to reduce further deposition in the new vicinity thereto. Another theory is that the molecule attaches itself to the cathode but allows the penetration of cathode electrons which charge it. There is then a combination with hydrogen ions from the solution and the hydrogen atoms thus formed to travel through the solution without impinging on the cathode and thus reducing stress. Although a number of polar groups have been tried for stress control such as OH, SO H, NO, NH COOH, and

6 CH CO, saccharin has been found to be the most effective.

It should be understood that the specific apparatus herein illustrated and described is intended to be representative only, as many changes may be made therein without departing from the clear teachings of the invention. Accordingly, reference should be made to the following claims in determining the full scope of the invention.

What is claimed is:

1. A method of making a memory matrix structure comprising:

disposing a set of bare conductors perpendicularly to a second set of insulated conductors, said sets being in substantial mechanical contact to provide two junction areas each defined by a bare conductor and an insulated conductor; masking the junction areas; applying insulation material to the unmasked area; removing the masking;

applying a conductive material to said junction areas to encircle the conductors at the junction area to form a mechanical connection of the set of the bare conductors; connecting the ends of the set of bare conductors together to form an electrodepositing cathode array;

electrodepositing magnetic material about the junction areas by using the connected ends of the bare conductors as a cathode,

and disassembling the cathode array by separating the connected bare wire ends to form a magnetic memory.

2. The method of claim 1 wherein the group of materials forming the conductive film consists of silver, copper, conductive epoxys and conductive paints.

3. The method of claim 1 wherein is included the step of bending the conductors of one set at the junction area to provide a short length of parallelism between the pairs of conductors at the junction area, which conductors otherwise remain generally perpendicularly disposed to the other set of conductors.

4. The method of claim 1 prior to said disassembly step wherein a plurality of steps of alternately applying a conductive film and electrodepositing magnetic material are provided.

5. The method of claim 1 wherein the magnetic material or magnetic alloy consists of a material selected from the group of nickel alloy, molybdenum alloy, cobalt alloy, and iron alloy.

References Cited by the Examiner UNITED STATES PATENTS 2,981,932 4/1961 Looney et al 340174 3,102,999 9/1963 Bernemy-r et al. 340-174 3,154,840 11/1964 Shahbender 29155.5 3,210,828 10/1965 Wendell 29155.5

JOHN F. CAMPBELL, Primary Examiner.

R. W. CHURCH, Assistant Examiner. 

1. A METHOD OF MAKING A MEMORY MATRIX STRUCTURE COMPRISING: DISPOSING A SET OF BARE CONDUCTORS PERPENDICULARLY TO A SECOND SET OF INSULATED CONDUCTORS, SAID SETS BEING IN SUBSTANTIAL MECHANICAL CONTACT TO PROVIDE TWO JUNCTION AREAS EACH DEFINED BY A BARE CONDUCTOR AND AN INSULATED CONDUCTOR; MASKING THE JUNCTION AREAS; APPLYING INSULATION MATERIAL TO THE UNMASKED AREA; REMOVING THE MASKING; APPLYING A CONDUCTIVE MATERIAL TO SAID JUNCTION AREAS TO ENCIRCLE THE CONDUCTORS AT THE JUNCTION AREA TO FORM A MECHANICAL CONNECTION OF THE SET OF THE BARE CONDUCTORS; CONNECTING THE ENDS OF THE SET OF BARE CONDUCTORS TOGETHER TO FORM AN ELECTRODEPOSITING CATHODE ARRAY; ELECTRODEPOSITING MAGNETIC MATERIAL ABOUT THE JUNCTION AREAS BY USING THE CONNECTED ENDS OF THE BARE CONDUCTORS AS A CATHODE, AND DISASSEMBLING THE CATHODE ARRAY BY SEPARATING THE CONNECTED BARE WIRE ENDS TO FORM A MAGNETIC MEMORY. 